Transcript Document
Welcome to Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the monthMarch 3, 2008 Dr. Uwe Trittmann Today’s Topics • Recent Advances in Astronomy – Part III • The Night Sky in March Recent Advances in Astronomy: Data • • • • Exoplanets discovered Kuiper belt objects discovered Age of the universe Temperature of the cosmic microwave background • Shape/Curvature of the universe • Acceleration of cosmic expansion • Nature of unknown content of universe How do we find Exoplanets? • Direct Observation (works only for double stars, planets are too dim) • Observe gravitational wiggles (Doppler effect) • Observe exoplanet transits (Brightness curve) • Or: Look them up on the internet ☺ http://exoplanets.org/ Direct Observation • Members of system are well separated, distinguishable • Works only for double stars, not planets Doppler Shift • Shift in optical frequency, analogy to shift in acoustic frequency shift (“emergency vehicle passing”) Doppler Detection • Example: • Jupiter's gravitational pull causes the Sun to wobble around in a circle with a velocity of 12 meters per second. Doppler Shift • Indirect observation by measuring the backand-forth Doppler shifts of the spectral lines Example: Exoplanet around HD 11964 • Doppler shift: Red Blue Doppler Detection: The Automated Planet Finder Telescope • “The Automated Planet Finder Telescope is optimized specifically for the Doppler detection of planets having masses 5 to 20 times that of Earth. Such planets would likely be rocky with atmospheres, and able to retain water. The 2.4meter, robotic, telescope will be dedicated every night to this planet search.” – http://exoplanets.org/telescope.html Eclipsing (Transiting) Exoplanets • Orbital plane of the planet need to be almost edge-on to our line of sight • We observe periodic changes in the starlight as the (dark) planet passes in front of the star Example: Amateur discovers Exoplanet Brightness/ time Kepler Satellite Mission • Detect Earthsize exoplanets by observing transits Exoplanet • SWEEPS-10 orbits its parent star from a distance of only 740,000 miles, so close that one year on the planet happens every 10 hours. The exoplanet belongs to a new class of zippy exoplanets called ultra-short-period planets (USPPs), which have orbits of less than a day. [Space.com] Exoplanet • Upsilon Andromeda b is tidally locked to its sun like the Moon is to Earth, so one side of the planet is always facing its star. This setup creates one of the largest temperature differences astronomers have ever seen on an exoplanet. One side of the planet is always hot as lava, while the other is chilled possibly below freezing. Exoplanet • The oldest known planet is a primeval world 12.7 billion years old that formed more than 8 billion years before Earth and only 2 billion years after the Big Bang. The discovery suggested planets are very common in the universe and raised the prospect that life began far sooner than most scientists ever imagined. Exoplanet • A year on HD209458b is only 3.5 Earth-days long. The planet orbits so close to its star that its atmosphere is being blown away by gales of stellar wind. Scientists estimate the planet is losing at least 10,000 tons of material every second. Eventually, only a dead core of the shrinking planet will remain. Exoplanet • HD 189733b was among the first planets to have its air “sniffed”. By analyzing light from the starplanet system, astronomers determined the planet’s atmosphere contains thick clouds of silicates similar to grains of sand. Curiously, no water vapor was detected, but scientists suspect it is hidden beneath the clouds. Exoplanet • Gliese 581 C marked a milestone in the search for worlds beyond our solar system. It is the smallest exoplanet ever detected, and the first to lie within the habitable zone of its parent star, thus raising the possibility that its surface could sustain liquid water, or even life. It is 50 percent bigger and 5 times more massive than Earth. What kind of exoplanets are we finding? • So far mostly “big Jupiters”, as expected • Two types of orbits: – Either highly eccentric and close to star – Or circular orbits and “typical” spacing Distances from Host Star Mercury Earth Jupiter Resonances • It seems that our solar system is very stable with respect to gravitational effects – The heavy planets are far out – The lighter planets are closer together – (Force of gravity grow with mass, decreases with distance) • This is no accident! If it weren’t like this, the big planets would gravitationally “bully” the others around: – Force them into eccentric orbits – Throw them out of the solar system A refined Picture • New picture emerges from lessons learned from exoplanets – Formation of a solar system is not necessarily the final word on appearance of a planetary system – Dramatic changes can happen in the millions of years • Collisions • Clean up • migration Heritage and History • How a planetary system looks like today is determined by how it formed AND what happened in its history • Our solar system seems to be protected from “drama” by its hierarchy and associated stabilizing resonances – Still: Jupiter probably migrated inward by throwing out lots of small bodies (“gravitational slingshot”) The Golden Age of Cosmology is – Now ! • Cosmology is one of the most exciting subfields of physics these days • The is an intimate connection between cosmology and particle physics • lots of data available and being measured • Today’s era is that of “precision cosmology” • There is lot’s we don’t know interesting for young scientists! Cosmology • Cosmology tries to understand how the cosmos itself changes • The universe is seen not as a canvas or stage on which things happen, but as a dynamical object, a “player” itself • The underlying theory is Einstein’s description of gravity, or … General Relativity! It’s easy! Rμν -1/2 gμν R = 8πG/c4 Tμν OK, fine, but what does that mean? (Actually, it took Prof. Einstein 10 years to come up with that!) The Idea behind General Relativity – In modern physics, we view space and time as a whole, we call it four-dimensional space-time. – Space-time is warped by the presence of masses like the sun, so “Mass tells space how to bend” – Objects (like planets) travel in “straight” lines through this curved space (we see this as orbits), so “Space tells matter how to move” Compare to Electrodynamics – In electrodynamics the two players are charges and electromagnetic fields. – Charges produce electromagnetic fields, so “Charges tell fields where and how to form ” – Electromagnetic fields exert forces on charges, so “Fields tell charges how to move” Here is a picture Sun Planet’s orbit Effects of General Relativity • Bending of starlight by the Sun's gravitational field (and other gravitational lensing effects) What General Relativity tells us • The more mass there is in the universe, the more “braking” of expansion there is • So the game is: Mass vs. Expansion And we can even calculate who wins! The Fate of the Universe – determined by a single number! • Critical density is the density required to just barely stop the expansion • We’ll use 0 = actual density/critical density: – 0 = 1 means it’s a tie – 0 > 1 means the universe will recollapse (Big Crunch) Mass wins! – 0 < 1 means gravity not strong enough to halt the expansion Expansion wins! • And the number is: 0 = 1 The Shape of the Universe • In the basic scenario there is a simple relation between the density and the shape of space-time: Density Curvature 2-D example Universe Time & Space 0>1 positive sphere closed, bound 0=1 zero (flat) plane open, marginal infinite 0<1 negative saddle open, unbound infinite finite The “size” of the Universe – depends on time! Expansion wins! It’s a tie! Mass wins! Time So, how much mass is in the Universe? • Can count all stars, galaxies etc. • this gives the mass of all “bright” objects • But: there is also DARK MATTER “Bright” Matter • All normal or “bright” matter can be “seen” in some way – Stars emit light, or other forms of electromagnetic radiation – All macroscopic matter emits EM radiation characteristic for its temperature – Microscopic matter (particles) interact via the Standard Model forces and can be detected this way First evidence for dark matter: The missing mass problem • Showed up when measuring rotation curves of galaxies Is Dark Matter real? • It is real in the sense that it has specific properties • The universe as a whole and its parts behave differently when different amounts of the “dark stuff” is in it • Good news: it still behaves like mass, so Einstein’s cosmology still works! Properties of Dark Matter • Dark Matter is dark at all wavelengths, not just visible light • We can’t see it (can’t detect it) • Only effect is has: it acts gravitationally like an additional mass • Found in galaxies, galaxies clusters, large scale structure of the universe • Necessary to explain structure formation in the universe at large scales What is Dark Matter? • More precise: What does Dark matter consist of? – – – – – Brown dwarfs? Black dwarfs? Black holes? Neutrinos? Other exotic subatomic particles? The Night Sky in March • Long nights, getting shorter! • Spring constellations come up: Leo, Cancer, Virgo, Big Dipper lots of galaxies! • Saturn & Mars are visible most of the night Moon Phases • Today (Waning Crescent) • 3 / 7 (New Moon) • 3 / 14 (First Quarter Moon) • 3 / 21 (Full Moon) • 3 / 29 (Last Quarter Moon) Today at Noon Sun at meridian, i.e. exactly south 10 PM Typical observing hour, early February Saturn Mars Star Maps Celestial North Pole – everything turns around this point Zenith – the point right above you & the middle of the map 40º 90º Due North Big Dipper points to the north pole West Perseus, Auriga & Taurus with Plejades and the Double Cluster SouthWest • Orion • Canis Major & Minor • Beautiful open star clusters • Orion Nebula M42 South • Gemini • Cancer • M44 Beehive (open star cluster) • Mars SouthEast Spring constellations: – Leo – Hydra M44 Beehive (open star cluster) Saturn East • Virgo & Coma High up in the East • Big Dipper • Bootes Mark your Calendars! • Next Starry Monday: April 7, 2008, 8 pm (this is a Monday ) • Observing at Prairie Oaks Metro Park: – Friday, February 15, 6:30 pm • Web pages: – http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.) – http://www.otterbein.edu/dept/PHYS/ (Physics Dept.) Mark your Calendars II • • • • Physics Coffee is every Monday, 3:00 pm Open to the public, everyone welcome! Location: across the hall, Science 244 Free coffee, cookies, etc.